PRODUCTION Of NUTRIENT SOURCES FOR RHIZOBIUM

dehydrogenase is used for the metabolism of mannitol or arabitol, whereas sorbitol is metabolized via
a specific sorbitol dehydrogenase. Another fast grower, R. trifolii, possesses five distinct polyol
dehydrogenases; inositol dehydrogenase for inositol; ribitol dehydrogenase for ribitol; D-arabitol
dehydrogenase for D-arabitol, D-mannitol, and D-sorbitol; xylitol dehydrogenase for xylitol; and Dsorbitol
and dulcitol dehydrogenase for dulcitol, ribitol, xylitol, and D-sorbitol. All polyols tested,
except xylitol and inositol, induced more than one polyol dehydrogenase. Glycerol supports the
growth of both fast and slow growers (Table 2). The metabolism of glycerol proceeds via glycerol
kinase and glycerolphosphate dehydrogenase, producing G3P that is further metabolized to pyruvate.
Both enzymes of glycerol metabolism are inducible, showing maximal activity with glycerol-grown
cells (Stowers, 1985).
Figure 1. The ketogluconate aldolase or Entner-Doudoroff pathway. G-6-P = glucose-6
phosphate; 6-P-G = 6-phosphogluconate; 2-K-3-D-6-PG or KDPG= 2-keto-3deoxy-6
phosphogluconate.
Source: Moat (1995).
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